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Each of these phenomena can boost or curb the effects of El Nino. But do they influence each other at a deeper level? Does El Nino trigger any of these other cycles? Is it triggered by them? To find out, Fairbanks turned to the Indian Ocean, where sea-surface temperatures, it turns out, rise and fall in response to both the monsoonal cycle and the El Nino cycle.
And as he and his colleagues reported in a recent issue of the journal Science, a 150-year-old coral from the Seychelles Islands perfectly preserves both sets of fluctuations. One pattern tracks the El Nino fluctuations, swinging back and forth every few years; the other rises and falls on a 12-year schedule that closely follows India's official monsoon-rainfall index.
What stands out in the data is an unusually sharp rise in sea-surface temperatures in 1877, the very year that a strong El Nino coincided with the greatest failure of the monsoon in recent times. "The way I think of it," says Fairbanks, "is as an orchestra. Sometimes the monsoon and El Nino play together, and sometimes they play apart. But where's the conductor?"
Where indeed? While all these climate cycles seem to involve both atmosphere and oceans, more and more scientists are abandoning their long-held belief that the former runs the show. The atmosphere is fickle, they observe. Storms form, then quickly dissipate, so whatever information they contain about the conditions that created them is quickly lost. By contrast, ocean gyres take anywhere from 10 to 20 years to complete a single journey, making them perfect vehicles for transmitting messages into the future. With the exception of the tropical Pacific, unfortunately, the oceans are even less well monitored than the surface of the moon. The changes they undergo, moreover, exceed any individual scientist's lifetime.
That's why corals and tree rings and ice cores are so important. They are like a tape recording of the various instruments in the climate orchestra, ranging from El Nino's high-frequency violin to the deeper cello- and basslike tones struck by longer-term cycles. By studying the hidden rhythms in these signals, scientists may finally be able to see how the parts fit together, sometimes harmonizing, sometimes clashing.
Over the next few years, Fairbanks hopes, he and others may shed light not only on El Nino's past but on its future as well. For if, as many experts expect, the atmosphere warms owing to the buildup of greenhouse gases, the El Nino cycle could very well change. But how? Would it speed up, slow down or stop entirely?
Given the present state of knowledge, no one can tell. The more scientists learn about the earth's climate system, the more complex and interconnected it seems, and the harder it is to unravel. That does nothing to diminish the tremendous advances that have occurred over the past decade. In fact, it is only because they have learned so much that scientists are finally ready to tackle the questions that the current El Nino has so eloquently framed--questions that may still be formidable, but perhaps no longer quite so intractable.
--With reporting by other bureaus